Android: modifying an XML element in a timer

Question

I am trying to have a counter (count seconds and minutes) and update it on the display every second.

I have this code in the onCreate of my class, which extends Activity:

timeOnCall = (TextView) findViewById(R.id.time);
minutes = seconds = 0;
timeOnCall.setText(minutes + ":" + seconds);

// Implements the timer
Timer timer = new Timer();
timer.scheduleAtFixedRate(new TimerTask() {
    public void run() {
        ++seconds;
        if (seconds == 60) {
            seconds = 0;
            ++minutes;
        }
        // Display the new time
        timeOnCall.setText(minutes + ":" + seconds);
    }
}, 1000, 1000);

Unfortunately, I get the following error:

android.view.ViewRoot$CalledFromWrongThreadException: Only the original thread that created a view hierarchy can touch its views.

I am not sure how to fix this as it's already in the onCreate() method. Does anyone know a solution?

Answer 1

You can do it with a handler, something lite this:

final Handler mHandler = new Handler();
final Runnable updateText = new Runnable() {
    public void run() {
        timeOnCall.setText(minutes + ":" + seconds);
    }
};

in onCreate you can then run:

onCreate(Bundle b) {
...
    Timer timer = new Timer();
    timer.scheduleAtFixedRate(new TimerTask() {
        public void run() {
            ++seconds;
            if (seconds == 60) {
                seconds = 0;
                ++minutes;
            }

            // Display the new time
        mHandler.post(updateText);
        }
    }, 1000, 1000);
}

Answer 2

Its because your trying to change the textview from inside a different thread. You can't do that. You need to post a message back to the thread that owns the textview.

public void run()

This starts a new thread that is separate from what is running your UI.

Edit: There are tons of examples online for the code you are looking for. Just Google something like "Android thread message handler."

Answer 3

Here is a complete step-by-step of what you are trying to do and doing it without a background thread. This is preferred over a timer because a timer uses a separate thread to do the update.

http://developer.android.com/resources/articles/timed-ui-updates.html